Climate Change and State Evolution

May 25, 2021 | Blog
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by Giacomo Benati (Eberhard Karls University Tübingen) and Carmine Guerriero (University of Bologna)

Ur Mosaic. Available at Wikimedia Commons

Despite the substantial evidence on the short run effects of adverse climate shocks, our understanding of their long run impact is limited.  To address such a key issue, research has focused on ancient societies because of their  limited economic complexity and their unparalleled experience of environmental and institutional change.  Notably, the ‘Collapse Archaeology’ literature has reported statistical evidence  consistent with the mantra that severe droughts trigger institutional crises.  This view, however, has recently been challenged by literature  summarized in our paper,  ‘Climate Change and State Evolution’ (PNAS.)

Using more detailed data on 44 major Bronze Age Mesopotamian polities and a more credible theory-based empirical strategy, our research project yields two novel empirical results. First, severe droughts encouraged the elites to grant strong political and property rights to the non-elites in order to persuade the latter that a sufficient proportion of the returns from joint investments would be shared via public good provision, thereby fostering a culture of cooperation.  Second, a more favourable climate allowed the elites to elicit cooperation under less inclusive political regimes, a weaker culture of cooperation and, possibly, incomplete property rights.

This second empirical result is consistent with the evolution of the earliest recorded forms of state institutions in Bronze Age Mesopotamia.  The increasingly cold and dry climate of the end of the Urban Revolution period (3800-3300 BCE) threatened consumption and thereby enhanced the importance of irrigation infrastructures.  The consequent need for labour-organization promoted a shift of decision-making power from the landholding groups to the temples.  Exploiting this new role, religious leaders obtained, over the Late Uruk period (3300-3100 BCE), command over public good provision and proposed a culture of cooperation in the provision of consumption risk-sharing activities: storing agricultural output, supplying grain in times of famine, regulating interest rates, and organizing craft activities.

Further evidence is provided by the droughts of the onset of the Early Dynastic period (3100-2550 BCE), when  declining  agricultural yields encouraged the temples to share their power with emerging palatial elites.  These elites exchanged tenure-for-service agreements for employment in public building projects and conscription.   Conscripted workers gained political power and benefitted from alternative means of consumption risk-sharing:  victuals, garments, access to irrigation,  draft animal power in peacetime, in addition to military spoils.  The formation of a conscripted army became the preferred public good for the non-elites.  Third, the more favorable climate of the pre-Sargonic period (2550-2350 BCE) curbed the elites’ need to entice the nonelites, easing the rise of royal ranks as supreme executive bodies. Also, the harsher climate of both the Akkadian and Old Babylonian periods (2350-1750 BCE), facilitated the emergence of long-distance exchange as an alternative to farming, and prompted the  elites to begin sharing their power with the merchant guilds to produce trade-related public goods. Finally, over the entire Bronze Age, adverse climate shocks were never so fierce as to impede any cooperation.

Two principal policy implications emerge from our research.  First, severe droughts depress the economy in the short run,  but over the medium to  long term they foster cooperation between the elites and non-elites which would otherwise have been unobtainable.   Cooperation is facilitated  by encouraging the participation of elites and nonelites in joint investments, which strengthens property rights.   Our analysis, based on ancient history, provides a framework which can be used  to assess the success of current responses  to the Covid pandemic.

Second, provided the political-economic environment generates a sufficiently large output for the population to share, less inclusive political regimes can nonetheless incentivize joint investments, especially if the non-elite appreciate the benefits of cooperation.

To conclude: our findings  support the proper combination of natural and social sciences when evaluating the total effect of major climate shocks.  Such an approach requires detailed and historically rigorous data on regional climate change, institutions,  economic outcomes, and   convincing theoretical models if we are to increase the credibility of empirical tests.


This study stems from projects conducted at the University of Bologna and funded through both the AlmaIdea 2017 and the Montalcini 2015 programmes.  We are grateful for the participation of  Federico Zaina (Polythecnic University of Milan) and Laura Righi (FSCIRE)  in these projects.


To contact the authors:

Giacomo Benati,
Carmine Guerriero,